Using Java 5 or Java 6 to prepare for SCJP 1.4 is not a good idea, because the newer versions of Java contain a number of new features, and the answers to some questions might be different if you use Java 5 or 6 instead of 1.4 (for example, questions that have to do with autoboxing - on Java 1.4, the correct answer would be "does not compile" while it would compile without errors on Java 5 or 6).